1. Field of the Invention
The present invention relates to a method for fabricating a liquid crystal display device whereby sealing material is applied to peripheral portions of two substrates of the liquid crystal display device.
2. Related Art
The liquid crystal cell is used as a display panel of a wristwatch, a desk top calculator, etc. A recent field of a use of the liquid crystal cell has been broadened to a mobile apparatus (an information terminal device) or a large size display device.
FIGS. 1(a)-(c) show a structure of a prior art liquid crystal cell formed by sealing the peripheral portions of two substrates face to each other by the sealing material, such as epoxy resin. FIG. 1(a) shows a plan view of the structure of one substrate of the liquid crystal cell. FIG. 1(b) shows a cross section along a cutting line A-A'. Particularly, in the FIG. 1(a), a pixel region 13, i.e. the display region, within the liquid crystal cell and the sealing scheme of the sealing material 30 are shown.
A first substrate 20 is made of a flat and hard glass plate. A major part of an upper surface of the first substrate 20 is the pixel region, i.e. the display region 13 on which colored layers forming R, G and B color filters (CF) are formed. The sealing material 30 is applied in a peripheral portion extending along the outer edge of the display region 13 of the first glass substrate 20 except a small portion which is later used as an entrance for the liquid crystal material. Small size spacers 40 are scattered on an entire area of the display region 13 to keep a thickness of a liquid crystal material to a constant value. A second substrate 10 is made of the flat and hard glass plate. A plurality of pixels, each of which includes a thin film transistor (TFT), are formed on the surface of the second substrate 10 to face each pixel on the first substrate 20. The second substrate 10 and the first substrate 20 are faced to each other, and the applied sealing material 30 is deformed to bond the two substrates 10 and 20. The sealing material 30, such as the epoxy resin, is cured by heating the bonded substrates and the liquid crystal cell is sealed. The liquid crystal material is put into the liquid crystal cell through the entrance by a method well known in the art, and the final product of the liquid crystal cell is completed.
The FIG. 1(c) schematically shows the deformed sealing material 30 on the corner region 42 during the sealing process in the prior art liquid crystal cell. Initially, the sealing material 30 on the corner region 42 is applied, as shown by hard lines 39. In the process for positioning the second substrate 10 on the sealing material 30, the sealing material on both the regions adjacent to the corner region 39 is moved and pressed toward the corner of the display region 13 resulting the pressed sealing material with an arc like edge 38 shown by a dash line.
The pixel region 13 in a side region 44 is generally formed to come near to an edge 36 of the sealing material 30 to insure the large display region 13. If the arc like edge 38 of the sealing material 30 in the corner region, however, extends toward the inside of the substrate 20, it covers the corner 15 of the pixel region 13. If the corner 15 of the pixel region 13 is covered by the sealing material 30, a defect of the displayed image is generated in the corner 15. To keep a good display quality in a corner region 42, it is necessary to keep away the corner 15 of the display region 13 from the inside edge 38 of the sealing material 30. In this case, however, it is required to broaden the space between the horizontal edge of the pixel region 13 and the inside edge 36 of the sealing material 30 to realize the large pixel region 13, resulting in that a use of a large substrate 20 is required.
Japanese Published Unexamined Patent Application 4-20929 discloses a liquid crystal cell in which an uneven portion is formed along peripheral portion of each of two substrates, a sealing material is applied on the uneven portion, and the two substrates are faced to each other and sealed. By providing the uneven portion on the portions on which the sealing material is applied, a strong adhesive strength is obtained, a penetration of water component into the liquid crystal cell is suppressed, and a reliability of a display panel is guaranteed.
Japanese Published Unexamined Patent Application 52-45947 discloses a technology for forming a groove along a peripheral edge of one of glass substrates of a liquid crystal cell. In a process for sealing the two glass substrates, an excess sealing material flows into the groove, so that a straight edge of the sealing material facing to a display area without an undesired wave like shape is realized. Since the edge of the sealing material facing to the display area is a straight line, a product value of the liquid crystal display panel is increased.
These prior art references, however, do not teach an improved method for applying the sealing material onto the corner regions of the substrate.
With the recent development of the mobile devices, such as a notebook computer, a personal data assistant (PDA), a handy phone, the requirement of the liquid crystal panel with the narrow frame region has been increased. To satisfy the technical requirement of the liquid crystal cell with the narrow frame region, it has been required to apply the sealing material used for sealing the two substrates onto the corner regions without partially overlapping with the corners 15 of the display region 13.
These prior art references discussed above do not teach a technology of the fabrication of the liquid crystal cell for narrowing the frame region surrounding the corner region of the display region.